Compositions of fluorocarbons



United States Patent Ollice 3,173,372 Patented Mar. 16, 1965 3,173,872COMPOIT10NS F FLUORGCARBGNS Robert D. Broadiey, Hanover Township, MorrisCounty,

NJ, and Lyman F. Kells, New York, N.Y., assignors to Allied ChemicalCorporation, New York, N.Y., a

corporation of New York No Drawing. Filed Mar. 12, 1962, Ser. No.17?,236

2 Claims. (Cl. 252-67) This invention relates to fluorinatedhydrocarbons, and more particularly to constant boiling fluorocarbonmixtures which comprise difiuorornethane and pertluoropropane and whichare especially adapted for use as high capacity, low temperaturerefrigeration compositions.

The refrigeration capacity of a given amount of re frigerant is largelya function of boiling point, the lower boiling refrigerants generallyoffering the greater capacity at a given evaporator temperature. Thisfactor to a great extent influences the design of refrigerationequipment and aifects capacity, power requirements, size and cost of theunit. Another important factor directly related to boiling point of therefrigerant is minimum cooling temperature obtained in the evaporatorduring the refrigeration cycle, the lower boiling refrigerants beingused to achieve the lower refrigeration temperatures. For these reasonsa large number of refrigerants of different boiling temperature andcapacity are required to permit flexibility in design, and the art iscontinuously faced with the problem of providing new refrigerants as theneed arises for new capacities and types of installations.

The lower aliphatic hydrocarbons when substituted by chlorine andfluorine are well known to have potential as refrigerants. Many of thesechlorofluorohydrocarbons exhibit certain desired properties includinglow cost, loW specific volume, low toxicity and chemical inertness whichhave resulted in the extensive use of such compounds in a large numberof refrigeration applications. Examples of such compounds includedifluorodichloromethane, B.P. 29.8 C., chlorodifiuoromethane, B.P. 40.8C., fiuorodichloromethane, BI. 89 C., fluorotrichloromethane, B1. 23.8"C., and tetrafluorodichloroethane, 13.1. 3.5 C. While thesechlorine-fluorine derivatives provide an adequate range of refrigerantsfor many purposes, only a very few boil sufficiently low to ofier anypotential as low temperature refrigerants. A major reason for this isthe presence of the heavier chlorine substituent which generally resultsin a higher boiling compound than those containing predominantlyfluorine or hydrogen.

A compound having considerable potential as a low temperaturerefrigerant is difiuoromethane, B.P. l.6 C. This fluorocarbon possessesmany of the desired properties for use in refrigeration notwithstandingthe presence of 2 hydrogen atoms which tend to induce flammability whichmay be objectionable in some refrigeration applications. Whilefiuorocarbons of this type are low boiling, the limited number of suchcompounds having the desired refrigerant properties represent widelydifferent boiling points and fail to provide a satisfactory ran e of lowboiling refrigerants of different capacity.

Increased activity in the field of cryogenics and low temperaturerefrigeration gives rise to a need for new low temperature refrigerantsrepresenting different capacities than now available. An object of thepresent invention is to provide new low temperature compositionsespecially suitable for use as refrigerants. More particularly, it is anobject to provide new refrigerants boiling lower and having greatercapacity than the low boiling difluoromethane. Another object is toprovide new low boiling compositions composed of difiuoromethanemixtures which are useful in producing refrigeration in those systems inwhich cooling is achieved by evaporation in the vicinity of the body tobe cooled. A further object is to provide low boiling difluoromethanecompositions in which the flammability is reduced to substantiallynegligible proportions.

In accordance with the invention it has been discovered thatcompositions consisting of difiuoromethane and approximately 10 molepercent to 62 mol percent perfluoropropane (C F B.P. 37.0 C. form amixture system of liquid compositions which have a boiling temperatureof about -58.1 C. These difluoromethaneperfiuoropropane compositionswith the -58.l C. boiling temperature represent a marked reduction ascompared with the boiling temperature of the lower boilingdifiuoromethane component. The indicateddifluoromethane-perfluoropropane compositions provide substantiallyincreased refrigeration capacity and represent new refrigerantcompositions useful in obtaining high capacity low temperaturerefrigeration. Further, flammability of difluoromethane is reduced byadmixture with perfiuoropropane such that all compositions within theindicated range are substantially non-flammable.

Boiling points of difluoromethane-perfiuoropropane mixtures weredetermined experimentally using difluoromethane and perfiuoropropaneeach better than 99.9% pure. Difluoromethane-perfluoropropane mixturesof known composition were prepared and boiling points were measured in avacuum jacketed boiling point tube under Dry Ice-acetone reflux.Temperatures were measured using a platinum resistance thermometer, andall determinations run in duplicate. The experimentally determinedboiling points were corrected to a normal atmospheric pressure of 760mm. of Hg and are sum marized below:

TABLE I Normal boiling points of CH F C 5 mixture system M01 percent C FNormal boiling in solution: point, C.

The data demonstrate that compositions consisting of difluoromethane andabout 10 mol percent to 62 mol percent perfluoropropane have the sameboiling tempera ture of about -5 8.1 C. The presence of a broad range ofcompositions havinng the same boiling temperature of 58.1 0.,representing a relatively marked depression of about 65 C. over that ofthe low boiling difiuoromethane component, indicated the difiuoromethaneand periluoropropane were only partially miscible within the indicatedrange and formed compositions having two liquid phases. Examination ofthe 9.9 mol percent and 61.7 mol percent perfluoropropane compositionsshowed the presence of two liquid phases and confirmed the formation ofa two-liquid phase system, while examination of the 1.7 mol percentperfluoropropane composition showed only a single liquid phase. We findthat when the two liquid phases are present, the entire range ofcompositions consisting of difluoromethane and approximately 10 to 62mol percent perfiuoropropane will boil at a substantially constanttemperature and give a constant vapor composition for the two-liquidphase compositions described.

Apart from use of the indicated amounts of difluoromethane andperfluoropropane make-up of the compo sitions of the invention requiresno special procedures. The difluoromethane and perfluoropropane employedshould be substantially pure, preferably at least about 9910 percentpure, and contain no substances deleteriously affecting the boilingcharacteristics of the mixture compositions or use as refrigerants. V

The minimum boiling two-liquid phase mixture system termed betweendifiuorornethane and perfluoropropane provides a broad range of mixturecompositions which boil at substantially constant temperature and give acon- 7 of difiuoromethane and perfiuoropropane, in which the stant vaporcomposition. These two-liquid phase mixtures differ from refrigerantmixtures proposed in the past which otfer only' a relatively narrowrange of useful compositions. Whileprior mixtures boil generally onlyabout 1-3? C. below the lower boiling component, the "mixture system "ofthe present invention results in a relatively large reduction ofabout'6.5 C. over the boiling point of difiuoromethane. The compositionsof the invention may be used in design of refrigeration equipment orreduced size operating at the evaporator tem- "peratures of about minus15 and below. to e.g.' minus The compositions of the'invention exhibitdesired refrigeration properties including low toxicity, chemicalinertness, and substantial non-flammability. In addition to being usefulas new refrigerants providing high camol percent of perfluoropropane iswithin the range of about l062. I

' 2; The process of producing refrigerationwhich comprises condensing amixture consisting of difiuoromethane and perfiuoropropane in which themol percent of per fluoropropane is within the range of about 10 62, andthereafter evaporating said mixture in the vicinityof a body to becooled. 7

References @ited in the file of this patent 'UNITED STATES PATENTS1,968,050 Midgley et al. July 31,1934 2,494,064 Simons et al Jan. 10,1950 2,687,441 Price et al. Aug. 24, 1954 3,018,306 Sweeney et al. Jan.23, 1962

1. A LOW BOILING COMPOSITION CONSISTING OF A MIXTURE OF DIFLUOROMETHANEAND PERFLUOROPROPANE, IN WHICH THE MOLE PERCENT OF PERFLUOROPROPANE ISWITHIN THE RANGE OF ABOUT 10-62.